Section one of the manual contains most of the commands which comprise the BSD user environment. Some of the commands included in section one are text editors, command shell interpreters, searching and sorting tools, file manipulation commands, system status commands, remote file copy commands, mail commands, compilers and compiler tools, formatted output tools, and line printer commands.
All commands set a status value upon exit which may be tested to see if the command completed normally. Traditionally, the value 0 signifies successful completion of the command, while a value >0 indicates an error. Some commands attempt to describe the nature of the failure by using errors codes as defined in sysexits(3), while others simply set the status to an arbitrary value >0 (typically 1).
apropos(1), man(1), intro(2), intro(3), sysexits(3), intro(4), intro(5), intro(6), intro(7), security(7), intro(8),